git/housekeeping: Reenable geometric repacking with alternates

When we first tried to roll out geometric repacking we quickly hit issues with them not working in the context of repositories which are connected to an alternate object database. The following investigation surfaced different errors in git-repack(1), git-pack-objects(1) and git-multi-pack-index(1) when alternates come into play. We have thus adapted the housekeeping strategy to only perform geometric repacking when the repository is not connected to an alternate object database.

Since then we have upstreamed a set of fixes which have been merged via de56e80363 (Merge branch 'ps/fix-geom-repack-with-alternates' into next, 2023-04-18). With these fixes applied, there are currently no bugs that would keep us from enabling geometric repacks in pooled repositories.

Enable geometric repacking in repositories which are part of an object pool when we detect that the current Git version has the fixes.

Closes #5034 (closed).